In general, a hybrid vehicle having a power-split powertrain does not need to control torque intervention since such a hybrid vehicle does not have a fixed gear transmission system unlike a transmission mounted electric device (TMED)-type hybrid vehicle or a conventional gasoline engine vehicle. However, when a traction control system (TCS) requests the torque intervention control, the hybrid vehicle having a power-split powertrain is required to control the torque intervention to limit a tractive force of vehicle wheels.
FIG. 1 is a view illustrating a control flow in a conventional TMED-type hybrid vehicle upon a request from a TCS.
An intervention torque that is smaller than a maximum output torque of a motor, as requested by a TSC, is controlled by the maximum output torque of the motor.
When the intervention torque is larger than the maximum output torque of the motor, whether the engine clutch is engaged is checked. If the engine clutch is engaged, some of the intervention torque is controlled by the maximum output torque of the motor, and the remaining intervention torque is controlled using an engine torque.
If such a conventional torque intervention control is applied to a power split-parallel hybrid, problems in vehicle operation occur.
FIG. 2 is a view illustrating a configuration of a power split-parallel hybrid vehicle. With reference to FIG. 2, problems with the application of the conventional torque intervention control to a power split-parallel hybrid vehicle will be described. In the power split-parallel hybrid vehicle, one planetary gear set (PG) is connected to an engine (E), a first motor generator (MG1), and a second motor generator (MG2), and transmits a torque through a sun gear (S), a carrier (C), and a ring gear (R). The torque, which is applied to each of the sun gear, the carrier, and the ring gear, is determined using the following equations.
            T      sun        =                  -                  1                      1            +            R                              ⁢              T        carrier                        T      out        =                            R                      1            +            R                          ⁢                  T          carrier                    +              T        ring                        T      ring        =          R      ·              T        sun                  R    =                  #        ⁢                  teeth          ring                            #        ⁢                  teeth          sun                    When the torque is not transmitted to each of the rotating elemental gears, not only a desired torque is not delivered to an output shaft, but also the sun gear and the carrier spin M freely.
If torque intervention is controlled by reducing a torque of the second motor generator (MG2), as in the TMED-type hybrid vehicle, an engine reaction torque from the second motor generator (MG2) and a reaction torque of the first motor generator (MG1), which is responsible for an engine speed control, are offset, thus causing a problem in operating the vehicle.
The matters described as the background arts are only intended to increase the understanding of the background of the present disclosure, but should not be recognized as being prior arts which are already known to those skilled in the art.